First HS2 'green tunnel' under construction to reduce railway impact on village and countryside

The first HS2 'green tunnel', designed to blend the high speed railway into the landscape, is under construction at Chipping Warden, near Banbury.

When complete, it will be covered by trees and shrubs to fit in with the surrounding countryside.

It is one of five 'green tunnels' on the HS2 route which aims to reduce disruption for communities.

The route is designed to improve links between London, Birmingham and the north, help level-up the economy and provide a low carbon alternative to car and air travel.

Measuring 1.5 miles long, the tunnel at Chipping Warden in Northamptonshire will be big enough to drive two double-decker buses through.

The tunnel will be built in sections, with construction expected to be complete in 2024.

A relief road has also recently been completed, which will take HS2 vehicles, and other local traffic, away from the centre of the village of Chipping Warden.

This will later be extended, to take the A361 over the top of the green tunnel.

• The green tunnels aim to reduce disruption for communities. Credit: HS2

Unlike a normal underground tunnel, it is being built on the surface using an off-site manufacturing approach, aiming to speed up construction and improve efficiency.

It means more than 5,000 giant concrete tunnel segments will be made in a factory in Derbyshire before being assembled on site.

Applying lessons from the construction of the latest French high speed lines, the off-site approach was developed by HS2’s main works contractor, EKFB.

The tunnel segments are being made by Stanton Precast in Ilkeston Derbyshire as part of a contract which is set to create up to 100 local jobs.

HS2 Ltd’s Project Client, Rohan Perin, said: "The Chipping Warden green tunnel is a great example of what we’re doing to reduce disruption for people living close to the railway and it’s fantastic to see the first arches in position.

"Our trains will be powered by zero carbon electricity but it’s also important to reduce the amount of carbon embedded in construction.

"The off-site manufacturing techniques being used will help cutting the overall amount of carbon-intensive concrete and steel in the tunnel and make the whole process faster, more efficient and therefore less disruptive for the community."

Designed as an m-shaped double arch, the tunnel will have separate halves for southbound and northbound trains, each one the height of two double-decker buses.

All 5,020 segments will be steel reinforced, with the largest weighing up to 43 tonnes.

HS2 says concrete and steel are some of the biggest sources of carbon emissions within the construction industry, so by reducing the amount of both materials needed for the tunnel, its lighter-weight modular approach is expected to more than halve the amount of carbon embedded in the structure.

The company adds that the approach also requires less people and equipment on site, improving safety and reducing disruption for residents.

EKFB’s Project Manager, Jeremie Martin, said: "Seeing the first set of precast units being installed is a milestone that the whole team is very proud of. 

"This three-year construction programme will benefit from off-site manufacturing making the green tunnel build more efficient than the traditional on-site building method.

"The HS2 green tunnels are a first of its kind in the UK. We have designed them as a twin arch ‘M’ shape which is more efficient than the standard box structure, reducing the amount of concrete required, which is a great example of how innovative engineering design can reduce carbon impact."

Similar green tunnels will also be built at nearby Greatworth as well as Wendover in Buckinghamshire and Burton Green in Warwickshire, stretching for a combined total of more than four miles.

The tunnels will all have specially designed ‘porous portals’ at either end to reduce the noise of trains entering and exiting the tunnel, along with small portal buildings to house safety and electrical equipment.

Tailored landscaping design plans will be developed for each tunnel, with thousands of native trees and shrubs typical to the local area such as Silver Birch, Oak, Beech and Willow planted to create new woodland areas around the portals and recreate the hedgerows and field boundaries on top of the tunnel.